LS Cooling Issue

[MotoWells]

Just completed an LS 6.2 swap in my 71 GMC

Unfortunately, I'm having cooling issues. I was hoping to get your thoughts on my setup.

I have a large capacity radiator with overflow and dual fans that seem to kick on ~200 deg. For now I am just using distilled water and a little coolant. Just started to run long enough to get an initial road test. On my recent road test the temp bounced from 180 all the way as high as 240 maybe even 260 and would not fall off while driving. This is obviously way too hot, dual fans come on etc. I suspect from reading other posts this could be due to an air pocket and that I need to "burp".

I also wanted to post some pictures of my setup in case something looks odd. Additional possible concerns - (overflow is to low, steam port is to low, steam port is introducing air, heater core has introduced air, wired dual fans with pigtail directly to GMPP controller cfan output)

Filled coolant through radiator not through engine hose. Never opened up heater until yesterday when heat started to climb.

Thanks for any thoughts or comments.

[mongocanfly]

yep...air pocket...common issue...remove top hose from the radiator and fill engine thru the top hose...I tied the hose up and just kept filling until it wouldn't take any more.make sure all air is out .then reinstall hose and you should be good..

[MotoWells]

Thanks for the quick response Mongo! I will attempt to fill through radiator hose and report back.

[72MARIO]

I had this problem on my last swap. Had to fill thru the hose and it took another gallon...

[Custom 68]

Yep that should take care of it. Just fill the block thru the upper hose.

[MotoWells]

Thanks guys, hoping to get out to the garage before Friday to test. I will be sure to give an update.

The little voice in the back of my head said you screwed up your new motor. Anyone know if these are fairly forgiving after running that kind of temp? It was not for long, maybe 6-7 miles before pulling back in the garage and washing down the rad with water.

[BR3W CITY]

Depends if your coolant sensor was reading a coolant temp, or trying to measure the temp of the air pocket. Do you have any signs of coolant coming out of places it shouldn't? (look for white residue on aluminum on the heads), and make sure there isn't any coolant in the oil. If you didn't pop an HG, your probably alright. When these get hot the ECM will pull a ton of timing to prevent det. and hitting the Kr* count.

Did is sputter/limp on its way home?

[MotoWells]

Everything seems to be ok, no coolant out of weird places that I can tell. Have not checked the oil for milkyness yet.

I had a faint hint of steam from the overflow at one point but that was a very limited time, maybe 1-2 minutes.

It did seem to detune a little right before I hit the driveway, not as perky as it was heading out but that could have been hypersensitivity to the situation. Figured if it did it was a fail-safe kicking in? I'm running the GMPP controller.

Thanks everyone!

[BR3W CITY]

Originally Posted by MotoWells

Figured if it did it was a fail-safe kicking in? I'm running the GMPP controller.

ECM sees high temp, tries to run all fans etc -> IAT's will increase, truck will start to adjust fuel to compensate -> Neither makes a difference, temps keep rising ->Coolant temps go above safety margin, vehicle goes in low-octane tables and tries to retard timing to prevent detonation -> Temps keep rising, most likely Kr* count is increasing, and the ECM will try to limp the truck.

Scan the ECM with a code reader and see what it threw. Then clear it all off ( half of the codes can be false triggers from the air bubble and temp issues.

I'd consider changing the oil out anyway, even if it looks ok.

[ls1nova71]

I'd say if it's running alright now then its going to be fine. I don't know how many people remember this, but GM themselves used to say in the brochure for the Camaro in about 98 or 99 that the LS1 was capable of being driven up to I think 50 miles with no coolant at all since the computer would deactivate cylinders to try and keep it cool. I never tried it, and they don't mention it anymore so not sure how true it is but I would think they did test it out and just dont say it anymore to keep idiots from doing it!

[MotoWells]

Worked on the truck today and unfortunately don't have much forward progress to report. Here is what I did.

1st - Unclamped the top hose and slowly filled the truck, went for ride with heater blasting and temp slowly climbed, longest its taken to get to 220 but it got to 220. Fans kicked on...

2nd - Parked at a significant incline with nose up. Stuffed a funnel down the radiator cap and slowly filled as temp rose. Shut it down, waited and then took it for a drive. Temp rose steadily until I pulled back into garage - 220-230 degrees - fans kicked on.

3rd - Pulled hoses off heater core. Made a loop back. Burped system, again using the top hose technique. Temp rose steadily, tried to burp any introduced air with funnel as well. Took out for a test spin, water quickly went to 180 and then slowly waltzed into 210-220...fans again.

4th and final - Pulled hose off the steam port and verified coolant was coming out as I topped off fill. Temp quickly climbed to 230...fans..shut it down and parked it.

Not much more time in day between waiting for cool downs. Any thoughts on what to try next?

Radiator is an RND Early Crossflow radiator with dual 12 inch fans. Both top and bottom hoses are on the same side. I pulled the lead from the GMPP controller and pigtailed to both fans, is that ok? They dont seem to pull a lot of air (cfm's) through the rad. I have a healthy 14 volts to the battery.

Some thoughts I had on next steps...

1 - Remove thermostat and attempt to run wide open?

2 - Should I get one of the special funnels made for burping air (image attached)?

3 - Get special controller from painless for wiring up fans (image attached)

4 - Replace RND fans with something else?

Thank you!

Jeff

[MotoWells]

One last thing I thought I would add that I forgot to mention in my update. The initial run I did after burping the coolant, I had the heater on full blast. That seemed to keep everything fairly happy at 200 if not a bit less for a majority of the time.

As I was getting closer to home I turned off the heater and the heat started to climb. Not sure if it was coincidence or not but the heater on full blast with initial run and burping did have the most stable results thus far.

[cooperhw]

Sounds to me like you might still have an air pocket in the back.
Best way I found to get "ALL" the air out is to remove the radiatior cap, open the overflow bottle lid, and take the steam port line off at the engine. Then jack the vehicle as high up in the air as possible so that the top the rad. cap is much higher than the rear of the motor. Fill all up and let it sit. about every 15 minutes add any water that it needs to keep it full. What this will do is allow the water near the top of the rad. to migrate into the back of the LS motor steam passages and it will displace (push) any trapped air towards the front and out the steam passage at the front of the motor. As soon as you see solid water coming out of the front steam passage you are done, put that line back on and lower the vehicle. Usually takes me about 30 minutes, and works every time.
If it's still going past 230 you have another problem, but 220 is fine with these motors. They like to run 220+ when AC is on.

[ls1nova71]

Originally Posted by MotoWells

One last thing I thought I would add that I forgot to mention in my update. The initial run I did after burping the coolant, I had the heater on full blast. That seemed to keep everything fairly happy at 200 if not a bit less for a majority of the time.

As I was getting closer to home I turned off the heater and the heat started to climb. Not sure if it was coincidence or not but the heater on full blast with initial run and burping did have the most stable results thus far.

If the heater core is stabilizing the temps then it sounds like your radiator is either not in the best shape/plugged up or you're not pulling enough air across it. Driving it at 45mph or higher would rule out if it's an air flow problem or not since the fans aren't needed above that.

[BR3W CITY]

Are you running the fans directly off the output wire on the GMPP controller? Does it require a relay? Running fans directly off the signal wire may not provide enough power.

Was it tuned at any point, or is the controller plug-n-play.

A cheapo ECM scanner from Harbor Freight will give you the codes. If you want to read/watch things like temp PID's, you'll need a more advanced scanner, or access to something like HP Tuners.

The heater core hoses come right off the waterneck where the Thermostat is, so it might be worth bypassing the heater core and seeing what changes.

[Hart_Rod]

Also, forgot to mention, cross check the Dakota Digital LED readout of the temp with what the analog gauge is saying. They should be pretty close.

[mongocanfly]

I just remembered also that my tuner guy had my fan settings messed up when he did my ecm...my ecm was from a truck and it wouldn't control 2 fans..I sent it back to him and he straightened it out...one fan would run full speed but fan 2 would just barely run..works great now..

[Custom 68]

one other thing, are you running the stock thermostat?

[MotoWells]

Wow, first off let me thank you all for your support and willingness to help.

I am running a stock GM harness, with stock settings. Looks like GM recommends to wire the fans direct from the wire provided off fuse block (image from documentation attached).

I am using Dakota digital VHX gauges with the BIM controller, this pulls the data right off the GM ECU through ODB II port.

I am running the stock thermostat.

Bypassed heater with no positive outcome.

Bottom hose is hot, top hose is hot as are both hoses for heater. Sounds like the thermostat is operating properly?

Fans come on but only one speed. Not sure if they can do two stages.

Starting to think the radiator or fans, I will attempt another burp session with an even more aggressive angle. Should I replace the thermostat with lower setting, maybe 160?

One thought, I could pull off the shroud and the two fans that came with the radiator. Put one large fan on and see what happens.


Thanks everyone!

[davepl]

Since I couldn't see the answer, I've got to ask a basic question: are the fans running at max?

If your engine is >220F and your fans aren't on, that's the problem. I'm guessing that's what's going on, and that you/we believe the engine ECM is not seeing the same temps as the gauge?

I would definitely get HPTuners or some kind of scan tool on there to see what the engine is seeing. You need to know if the fans are being commanded on, and if not, why not. And if they are, why they aren't running.

Unless the fans ARE running at max at that point, but I couldn't deduce that from my scan of the thread.

For my LS swap I let the stock ECM control the fan outputs and then connected those to a three-relay setup so that it runs them in stages:

- Both fans on LO
- One fan on HI
- Both fans on HI

Even with an old school BeCool aluminum radiator I had left over the from the old big block it never gets past the "One fan on HI" stage. I've never needed both fans yet, even in heavy stop and go traffic.

[davepl]

But does the fan run the way it is now? The fact that running the heater helped makes me think your main fan isn't even running, but I can't tell yet.

[MotoWells]

Originally Posted by davepl

But does the fan run the way it is now? The fact that running the heater helped makes me think your main fan isn't even running, but I can't tell yet.

Yes, fans come on, single speed at ~ 200-207 deg just like GM says they will but have only heard one speed. Seems like too little too late on the fans and fan speed. NO low then high speed that I can tell. Sorry, updated my response above to include this information.

Thank you

[Hart_Rod]

Originally Posted by MotoWells

Yes, fans come on, single speed at ~ 200-207 deg just like GM says they will but have only heard one speed. Seems like too little too late on the fans and fan speed. NO low then high speed that I can tell. Sorry, updated my response above to include this information.

Thank you

Factory fan settings on a truck:

Fan 1 on: 226F
Fan 1 off: 219F

Fan 2 on: 235F
Fan 2 off: 227F

[MotoWells]

Originally Posted by Hart_Rod

Factory fan settings on a truck:

Fan 1 on: 226F
Fan 1 off: 219F

Fan 2 on: 235F
Fan 2 off: 227F

Thank you, with my setup I do have two fans however the GM Controller I have has one wire. GM said to attach that single wire from their relay / fuse box to the fan. I pigtailed that to drive both 12 inch fans and ground both directly to battery.

[davepl]

Originally Posted by MotoWells

Thank you, with my setup I do have two fans however the GM Controller I have has one wire. GM said to attach that single wire from their relay / fuse box to the fan. I pigtailed that to drive both 12 inch fans and ground both directly to battery.

This is often true. On the GMPP LS3 controller, for example, the wiring harness they give you has the two fans (blue and green wires, if I recall correctly) tied together so that it's just one output.

I went into my harness and split the wires and then into the code and split the ON temps, but some harnesses come with them bundled together, which is fine, you just treat them like one fan.

So ignore my stuff about HI/LO and split operation - your fan should come on at 207 (or whatever) at FULL speed.

Just as a random though - the later ones, like the LT1 and LT4, use a PWM (pulse width modulation) fan control scheme, meaning they use a high power transistor and they turn the fan motor off and on a hundred time s a second (or whatever) to give them speed control. That wouldn't work through another relay, so if you had that setup (and I do not know which you have), you couldn't use an additional relay, you'd need to use the wire from the ECM. I only mention it because some people use the fan control wire to trigger another relay, which doesn't work with PWM. But that's only on the fairly newest ECMs I think.